The present invention relates to a read-out device for information stored in a phosphor carrier, and to an x-ray cassette. In particular, the present invention relates to a device for the line by line read out of information, such as x-ray information, stored in a phosphor carrier. The information is read out using a radiation source that can generate several individual beams, each of which stimulates the phosphor carrier such that it emits secondary radiation. The secondary radiation, which contains at least a partial reproduction of the stored information, is received at a plurality of point elements of a receiving device. The x-ray cassette includes the phosphor carrier and is designed for writing x-ray information onto this phosphor carrier.
Especially for medical purposes, x-ray radiation is used to generate an image of an object, for example a patient, where said image is stored as a latent image in a phosphor carrier. The phosphor carrier is stimulated using the radiation source to read out the x-ray image stored in the phosphor carrier. According to the stimulation, it will emit light with an intensity in proportion to the x-ray image stored in the phosphor carrier. The light emitted by the phosphor carrier is received by a detection device, causing the x-ray image stored in the phosphor carrier to be made visible. For example, the x-ray image may be presented directly on a monitor. On the other hand, it is possible to write the x-ray image on a photographic x-ray film specifically manufactured for x-ray images.
An apparatus for reading out information stored in a phosphor carrier is known from the Published European Patent Application No. EP 0 777 148 A1. In this known application, the phosphor carrier is stimulated by a laser beam. Using a very fast rotating polygon mirror and several optical lenses, the laser beam of a single laser is directed to the phosphor carrier. The apparatus described in the patent application is a so-called xe2x80x9cflying spotxe2x80x9d scanning device, where the laser beam reflected by the polygon mirror stimulates all points of a line of the phosphor carrier in sequence. The light emitted by the phosphor carrier due to the stimulation with the laser beam is guided by a fiber cross-section converter to a photoelectric sensor that converts the collected photons into electrical signals.
Using this apparatus, only one single point of the phosphor carrier material at a time is stimulated to emit light. To be able to read out the entire information stored in the phosphor carrier in an acceptablexe2x80x94that is, a relatively shortxe2x80x94time period, the individual points of the phosphor carrier can be stimulated only briefly. A typical stimulation time for xe2x80x9cflying spotxe2x80x9d systems is about 6 xcexcs for one point. Because of this brief time period of stimulation, the intensity of the laser beam generated by the laser must be very high for the individual points of the phosphor carrier to be able to emit a sufficiently strong radiation. In addition, only a relatively small amount of the stored information can be read out. This limits the attainable quality for reproducing the stored information.
The laser beam stimulating the phosphor must fulfill certain conditions with regard to spatial and spectral distribution. Such xe2x80x9cflying spotxe2x80x9d systems require a laser beam guidance with a length of 1.5 to 2 times the width of the line of the phosphor carrier that is to be stimulated, especially to be able to stimulate the entire width of the phosphor carrier. Focusing and guiding the laser beam requires a very sophisticated and, thus, cost-intensive system of optical components. Furthermore, these optical components require considerable space such that the instrument dimensions of such a xe2x80x9cflying spotxe2x80x9d system are very large.
It is a principal objective of the present invention to ensure good quality when reproducing information stored in a phosphor carrier.
This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by providing a radiation source which includes an optical device for expanding the several individual beams in the direction of a line on the phosphor carrier.
According to the invention, the receiving device is designed such that it contains a multitude of point elements and where the secondary radiation emitted by the stimulated points of the phosphor carrier can be received, point by point, simultaneously by several of these point elements. A specified minimum energy E is required to stimulate the individual points of the phosphor carrier such that they can emit this secondary radiation. This energy is proportional to the power (intensity) of the radiation source and the dwell time of the primary radiation emitted by the radiation source at the point of the phosphor carrier to be stimulated. If several points of the phosphor carrier are stimulated at the same time, it is possible to attain a relatively long dwell time of the primary radiation for each point of the phosphor carrier, without prolonging the overall time for reading out the entire information stored in the phosphor carrier. Moreover, it is advantageously even possible to shorten this overall time for reading out the entire information stored in the phosphor carrier. Due to the long dwell time at each point of the phosphor plate, the scanning speed for stimulating the points of the phosphor plate can be kept low. Each point emits a large secondary radiation that can be detected by the receiving device.
It is possible to integrate the secondary radiation emitted by the phosphor carrier over a long time period. Since each point element of the receiving device exhibits a certain background noise, the signal to noise ratio of the point elements can be increased advantageously based on the invention. Due to the longer dwell time of the primary radiation of the radiation source per point of the phosphor carrier, it is also possible to reduce the power (intensity) that needs to be generated by the radiation source and to still generate the required energy E for stimulating the phosphor carrier.
In an advantageous embodiment of the invention, it is possible to simultaneously stimulate several points, in particular, all points that are arranged in a line of the phosphor carrier. In doing so, it is possible to stimulate a large number of points of the phosphor carrier simultaneously and at the same time keep the expenditures for the design of the radiation source and the receiving device relatively small. Thus, the required number of components in the radiation source and the receiving device can be limited. This ensures a great compactness of the device.
Advantageously, several individual beams can be generated by the radiation source, which makes simultaneous and precise stimulation of several points of the phosphor carrier simple and effective.
An advantageous design of the radiation source exhibits several laser diodes that are used for the stimulation of the several points of the phosphor carrier. Laser diodes can generate sufficient radiation power for stimulating the points of the phosphor carrier. At the same time, they are very compact, such that they are conducive for the design with small dimensions of the device subject to the invention. In addition, laser diodes are easy to control.
In a particularly advantageous design of the invention, the number of laser diodes in the radiation source is equal to the number of point elements of the receiving device. In this case, each point of the line of the phosphor carrier to be stimulated is stimulated simultaneously. The radiation source is then designed as a line of laser diodes. In this manner, it is advantageously possible to do without additional optical means for expansion and focussing of the laser diode beams. The distance between the radiation source and the phosphor carrier to be stimulated can be kept small, which further adds to the compactness of the device.
To be able to stimulate several points of the phosphor carrier with one single beam, the radiation source may be equipped with an optical system with which the single beam can be expanded in the expansion direction of a line of the phosphor carrier. In this manner, it is also advantageously possible to overlap several single beams, especially two single beams at least partially on the respective point of the phosphor carrier to be stimulated. The stimulation power to be generated by the radiation source can be reduced using this overlapping of the intensities of several individual beams. Furthermore, the read-out reliability is increased in case one single beam malfunctions. To limit the single beams despite the expansion in the expansion direction of one single line to this line, the optics provided in the radiation source is advantageously designed such that it focuses the single beams in a direction perpendicular to the direction of expansion of the line. This ensures that an unintentional stimulation of lines that are adjacent to the line to be currently stimulated is avoided.
A reproduction device can be provided between the phosphor carrier and the receiving device, which can be used to reproduce the secondary radiation emitted by the individual stimulated points of the phosphor carrier at the individual point elements of the receiving device. Advantageously, this reproduction is carried out on a 1:1 scale. In this manner, the use of a fiber cross-section converter with its disadvantageously large dimensions can be avoided. This results in a very short distance between phosphor carrier and receiving device, which in turn greatly improves the degree of compactness of the device.
Two radiation sources are provided in another particularly advantageous embodiment of the invention, where one receiving device each is assigned to said radiation sources. The two radiation sources and their associated receiving devices are arranged such that the phosphor carrier, which is designed as a phosphor plate with a top and a bottom side, can be read out from both sides. This can further increase the amount of secondary radiation to be emitted by the phosphor carrier, which in turn improves the quality of the reproduction of the information that is to be read out from the phosphor plate.
According to the invention, a device for reading out information stored in a phosphor carrier is arranged directly in an x-ray cassette that exhibits such a phosphor carrier. X-ray information stored in the phosphor carrier can then be read out directly from the device subject to the invention and provided to a control device for further processing. Advantageously, such an x-ray cassette can be integrated directly in an x-ray unit. To read out the information stored in the phosphor carrier, it is advantageously no longer required for the operating personnel to remove the x-ray cassette from the x-ray unit and insert it in a special reading device for reading out the stored information. This significantly improves the operating convenience.
In one advantageous embodiment of the x-ray cassette subject to the invention, a phosphor carrier is designed as a phosphor plate that exhibits a top and a bottom side that have coatings that are different from one another. These two different coatings exhibit different sensitivities. For example, using the coating of one side of the phosphor plate, bones can be recorded better while the coating on the other side of the phosphor plate, may be better suitable to record soft parts. This gives the operator the selection between two sensitivities based on this design of the x-ray cassette subject to the invention. This allows for increased flexibility and capability of the device subject to the invention.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.